$\begin{cases}a(1)=-13\\\\ a(n)=a(n-1)+4 \end{cases}$ Find the $2^{\text{nd}}$ term in the sequence.
Explanation: This is a recursive formula. It tells us that the first term is $-13$ and that the common difference is $4$. $\begin{aligned} {a(1)}&=-13 \\\\ {a(2)}&={a(1)}+4=-9 \end{aligned}$ The $2^{\text{nd}}$ term is $-9$.